Biomaterial-centered infection is a prevalent cause of revision surgery in general and particularly in total joint replacement. Revision surgeries due to infection are risky and invasive. Conventionally, if an infection occurs after a total joint replacement, bone ingrowth is inhibited by bacteria, and the responsible implant must be removed and replaced with a temporary implant composed of anti-infection agents. During this time, a patient has an extensive stay in a hospital or is otherwise rendered immobile because the temporary infection-fighting implant is typically non-load bearing. In some instances, a patient may be confined to a bed or wheelchair for weeks before the infection is stopped. When the infection subsides, the temporary infection-fighting implant is removed and a revision implant is inserted in its place. This procedure is costly to the patient in both time and money. Infections associated with inserting a medical device can be devastating, painful, and cause prolonged disability. Treating the infection may cost tens of thousands of dollars. Moreover, surgeons are presented with greater risks if post-operative infection occurs.
Conventionally, certain precautions are taken to prevent post-surgery infection. For example, antibiotics are provided to a patient before and after surgery to reduce the risk of infection. Antibiotics are typically given within one hour of the start of surgery (usually once in the operating room) and continued for a short period following the procedure. Short operating time and minimal Operating Room (OR) traffic may further reduce the risk of infection during surgery, such as a total joint replacement procedure or an intramedullary nailing procedure. By increasing efficiency in the OR, a surgeon may effectively lower the risk of infection by limiting the time the anatomy is exposed. Limiting the number of operating room personnel entering and leaving the operating room is also thought to decrease risk of infection. Another precaution is the strict adherence to sophisticated sterilization techniques. However, despite the aforementioned precautions being taken, post-surgery infection remains a real and serious threat.
There are generally two types of post-surgery infections. First, early-stage infection occurs in the weeks following surgery and may sometimes be cured with a surgical washout and intravenous antibiotics. The exact period of surgical washout necessary is debatable but is typically between about three to about eight weeks. It is, however, generally accepted that curing an infection without removing the responsible orthopaedic implant becomes harder and harder with each passing day after surgery. Second, late-stage infection usually occurs after months or even years after surgery and almost always requires removal of the orthopaedic implant. An “antibiotic spacer” is placed into the void and intravenous antibiotics are provided to the patient. Patients with late-stage infection may need to undergo at least six weeks of intravenous (IV) antibiotics, possibly more, before the orthopaedic implant can be replaced.
In the area of orthopaedics, the prior art has attempted to coat implants with antimicrobial products to prevent infection (see e.g. “Antibacterial Nanosized Silver Substituted Hydroxyapatite: Synthesis and Characterization,” by Rameshbabu et al. (2006); “In Vitro Anti-bacterial and Biological Properties of Magnetron Co-sputtered Silver-containing Hydroxyapatite Coating,” by Chen et al. (2006); “Antibacterial Effects of Ag-Hap Thin Films on Alumina Substrates,” by Feng et al. (1998)).
U.S. Pat. No. 6,719,987 issued on Apr. 13, 2004 to Nucryst Pharmaceuticals Corp. of Alberta, Canada discusses antimicrobial coatings or powders that provide an effective and sustainable antimicrobial effect. The '987 patent is herein incorporated by reference in its entirety.
U.S. Published Patent Application No. 2004/0074568A1 published on Apr. 22, 2004 discusses an anchor module for covalently bonding a mediator module, such as an antibiotic, to a medical implant. The disclosure of the '568 Publication is herein incorporated by reference in its entirety.
U.S. Published Patent Application 2006/0286140A1 published on Dec. 21, 2006 discusses a medical implant with therapeutic molecules bonded to its surface. The disclosure of the '140 Publication is herein incorporated by reference in its entirety.
In vitro cell culture studies have shown that low concentrations of silver may reduce the risk of infection. Thus, with the onset of multi-drug resistance in many bacterial strains, a new treatment methodology with the powerful antibacterial properties of silver at low concentrations has been sought. For example, U.S. Pat. No. 5,151,122, issued on Sep. 29, 1992, suggests adding any one of copper, silver, or zinc to a hydroxyapatite coating in order to provide antibacterial effectiveness. Similarly, U.S. Pat. No. 5,266,534, issued on Nov. 30, 1993, suggests adding silver and silicon to an HA coating. U.S. Pat. No. 5,348,577, issued on Sep. 20, 1994, further suggests adding silver and zinc for antibacterial purposes. U.S. Pat. No. 5,268,174, issued on Dec. 7, 1993, suggests an antimicrobial hydroxyapatite powder composition having zinc and further including fluoride for its bone-stimulating properties. U.S. Pat. Nos. 5,151,122, 5,266,534, 5,348,577, and 5,268,174, are incorporated by reference as though fully set forth herein.
The present invention discusses an implant which aims to improve at least one of the problems of the prior art.